Different types of battery implementations are known in the art, e.g., battery cells, battery packs, battery modules, etc. Furthermore, these various implementations may be available in different shapes such as cylindrical, pouch/prismatic, coin or button, etc., and moreover, the different batteries may also operate under different chemistries. However, a common feature among all batteries is that they store energy in the form of chemical and electrochemical reactions.
Thus, during operation of a battery (i.e., as the battery is charged or discharged), heat is produced within the battery wherein the reactions take place. If the battery is operated at low power (i.e., low currents), it is possible for a substantial portion of the heat that is generated to be conducted away, while at most a minor amount of heat may be accumulated. Heat accumulation in this manner may cause the temperature of the battery to only increase slightly, without significant effects on operation of the battery. On the other hand, if the battery is operated at a higher power, the heat may be generated more rapidly. In case the heat is generated more quickly than it can be conducted away or dissipated, the accumulation of heat can cause the temperature of the battery to increase to undesirable levels.
If the internal temperature of a battery becomes too high, the health and future performance of the battery can be negatively impacted. For example, due to high heat accumulation, organic electrolytes found in several types of batteries may decompose; polymer binders or membranes in batteries may melt; internal components of batteries may degrade; or other unwanted side reactions may take place. In extreme scenarios, catastrophic failure such as explosions or battery fires can also occur
It is recognized that the temperature increase as noted above may not take place in a uniform manner across the body of the battery. Local inhomogeneities in the rate of electrochemical reactions can cause local temperature spikes, especially during high-rate, high-power operation. Internal short circuits may also cause local spikes in the temperature of the battery. These concerns are viewed as being increasingly important in view of the strong push towards designing batteries that can be safely charged and/or discharged at a fast rate.
In general, the temperature of a material or medium is related to the speed at which the constituent molecules making up the material or medium are vibrating. Thus, measuring the temperature of the material or medium is measured, may be effectively viewed as sampling the local vibrations at the measurement location. Conventionally, the temperature of a battery (typically during operation) is measured at a surface of the battery, using devices such as thermocouples, thermistors, resistance thermometers, silicon bandgap temperature sensors, thermal cameras, or fiber-optic gratings. A key deficiency associated with such methods is that heat is generated internally, e.g., at the electrodes where the electrochemical reactions take place, and thus the surface measurements may not be accurate. To explain further, in order to make these conventional measurements with state-of-the-art methods, the internally generated heat must first travel to the surface of the battery before the heat can be measured. Thus, surface measurements can lead to inaccuracies in both the spatial resolution and the temporal sensitivity of the temperature measurement. These drawbacks can be especially problematic if a device used for the temperature measurement is integrated into a control system or failure/fault warning system configured to detect and raise alarms or trigger corrective actions, for example, because the device would not be able to faithfully and correctly collect the requisite data.
Accordingly, there is a need recognized in the art for accurate temperature measurement techniques for batteries and internal components thereof.